Chemical composition of lipophilic extractives released during the hot water treatment of wheat straw

Treatment of wheat straw with hot water at 80-95 degrees C for 0.5 h at pH 6.0-8.0 released 41.0-53.0% of the original lipophilic extractives. The chemical compositions of six lipophilic extractives were determined by GC on a medium-length high-temperature capillary column without derivatization, thus giving a method for direct determination of individual components of free fatty and resin acids, sterols, waxes, sterol esters, and triglycerides. The extracts contained 68.7-75.8% lipophilic substances, comprising mainly free fatty acids (25.8-48.4%), waxes (9.4-27.0%), sterols (4.1-8.0%), triglycerides (3.3-11.0%), and sterol esters (2.6-5.1%). Minor amounts of diglycerides (0.3-0.5%), resin acid (0.5-3.1%), and phenolic compounds (0.9-3.6%) were also quantitatively determined in the extractives.     

Biodegradation of aspen steryl esters and waxes by two filamentous fungi with or without other carbon sources

Aspergillus luchuensis and Cunninghamella elegans were evaluated for their growth on steryl esters and waxes, which are a major cause of pitch deposition in aspen pulping. These fungi hydrolysed aspen steryl esters and waxes into their constituent sterol and fatty acid moieties. A. luchuensis and C. elegans were also grown on steryl esters and waxes supplemented with glucose and triglycerides in order to provide a more accurate assessment of how these fungi behave on aspen wood. Both fungi consumed glucose before steryl esters and waxes while they degraded the triglycerides and steryl esters and waxes simultaneously.     

Chromatography of unusual lipids on thin layers of magnesium oxide

The chromatographic behavior of some minor components of natural lipids was studied using layers of magnesium oxide and of commercial adsorbents containing magnesium oxide. The lipids investigated included wax esters, cholesteryl esters, diester waxes, and esters, ethers and ether-esters of ethanediol and glycerol. Pronounced differences were found in the patterns of separation of certain lipids on magnesium oxide as compared to silica gel and Florisil. The procedures described afford means for the detection of unusual lipids in natural materials, and their isolation.     

Plumage reflectance is not affected by preen wax composition in red knots Calidris canutus

It has recently been shown that sandpipers (Scolopacidae) abruptly switch the chemical composition of their preen gland secretions from mono- to diester waxes just before the period of courtship. The timing and context of the shift suggested that diesters could provide a visible quality signal during mate choice. We used captive red knots Calidris canutus to test whether mono- and diester preen waxes affect the light reflectance ("colour") of the plumage. We also determined light absorbance spectra of the two wax types. The reflectance of breast feathers of the breeding plumage was measured with spectrophotometry when birds secreted monoesters and six weeks later when they secreted diester preen waxes. Light reflectance was also measured after removing the mono- and diester waxes from the plumage with a solvent. The results show that: (1) diester preen waxes absorb more light, especially ultraviolet (UV), than monoester preen waxes, but that (2) the compositional shift in the preen waxes did not change plumage reflectance and, (3) the removal of preen waxes did not change the reflectance of the plumage within the light spectrum assumed visible to birds (320–700 nm). This is not consistent with the idea that compositional shifts in the preen waxes of red knots have a visual function.     

Lipase hydrolysis of mammalian long-chain 1,2-alkanediol diesters. Nonrandom distribution of fatty acids

Long-chain 1,2-alkanediol diesters were isolated from the total surface lipids of golden Syrian hamsters and Swiss albino mice. Hydrolysis of the diol diester waxes with exocellular lipase from Rhizopus arrhizus delemar or with purified porcine pancreatic lipase produced free fatty acids and 2-acyl diols in about 60--80% yield. Nonrandom distribution of the constituent fatty acids at positions 1 and 2 of the alkanediols was observed. In the diester waxes from the hamster, both straight-chain and branched-chain fatty acids of 14 to 20 carbon atoms predominated at position 1 and those of 22 to 26 carbon atoms at position 2. In contrast, the diester waxes of the mouse contained mainly fatty acids of less than 19 carbon atoms, both saturated and monounsaturated, at position 2 and those of greater chain length (20 to 24 carbon atoms) at position 1. The results of the lipase hydrolysis were confirmed by degradation of the diester waxes with Grignard reagent.     

An avian equivalent of make-up?

We report that a long-distance migrating shorebird, the red knot, makes a complete switch from commonly occurring monoester preen waxes to a much rarer class of higher-molecular-weight diester waxes at the time of take-off to the high arctic breeding grounds. The cold arctic climate would have required a lowering of wax-viscosity, and thus, a shift in the reverse direction. We propose that a sexually selected need for a brilliant plumage has lead to this conter-intuitive temporary shift from monoesters to diester waxes. The difficulty of application of the diester preen waxes under cold conditions would ensure the reliability of the quality-signalling function of this most probably sexually selected trait.     

Sandpipers (Scolopacidae) switch from monoester to diester preen waxes during courtship and incubation,but why?

Recently, a shift in preen wax composition, from lower molecular weight monoesters to higher molecular weight diesters, was described for individuals of a sandpiper species (red knot, Calidris canutus) that were about to leave for the tundra breeding grounds. The timing of the shift indicated that diester waxes served as a quality signal during mate choice. Here, this hypothesis is evaluated on the basis of a survey of preen wax composition in 19 sandpiper species. All of these species showed the same shift observed in the high-Arctic breeding red knots. As the shift also occurred in temperate breeding species, it is not specific to tundra-breeding sandpipers. Both sexes produced the diester waxes during the incubation period until hatching, in addition to the short period of courtship, indicating that diesters' functions extend beyond that of a sexually selected 'make-up'. The few non-incubating birds examined (males of curlew sandpipers (C. ferruginea) and ruffs (Philomachus pugnax)) had the lowest likelihood of secreting diesters, indicating a functional role for diester preen waxes during incubation. We propose that diester preen waxes enhance olfactory crypticism at the nest.     

Estradiol induces proliferation of peroxisome-like microbodies and the production of 3-hydroxy fatty acid diesters, the female pheromones, in the uropygial glands of male and female mallards

During the mating season the female mallards produce sex pheromones, diesters of 3-hydroxy fatty acids, in their uropygial glands. Subcellular fractionation by sucrose and Nycodenz density gradient centrifugations and electron microscopic examination of the fractions showed that diesters of 3-hydroxy acids and the enzymes that catalyze the formation and esterification of the 3-hydroxy fatty acids are located in the catalase-containing fractions, probably peroxisomes, whereas monoester synthesizing activities are located in the endoplasmic reticulum. Fatty acyl-CoA reductase that would provide fatty alcohol needed for the synthesis of monoester and diester waxes was found both in the peroxisomal and endoplasmic reticulum fraction. Upon daily intramuscular injection of estradiol into the females in the nonmating season, the short chain monoester waxes of the uropygial glands were replaced by long chain monoester waxes, and subsequently the monoester waxes were replaced by diester waxes. Injection of thyroxine with estradiol hastened the induction of the compositional changes including diester synthesis. Similar changes, including the synthesis of the female pheromones, were induced in the uropygial glands by the hormone treatment of males that do not normally produce diesters at any time during their life cycle. The structure and composition of the diesters induced by hormone treatment of both males and females were identical to those of the female pheromones produced during their mating season. Electron microscopic examination of diaminobenzidine-treated glands showed that peroxisomes proliferated in the gland of the females in the mating season and in the estradiol-treated males that produce the diesters.     

Parental role division predicts avian preen wax cycles

Previous studies have shown that preen wax composition in some sandpipers shifts from the usual monoesters to diesters during the breeding season, possibly to reduce the ability of mammalian predators to find nests using olfactory cues. To investigate further the relationship between incubation and wax secretion, we examined seven sandpiper species with different incubation patterns (species in which both sexes incubate, in which only males incubate and in which only females incubate). During the breeding period, diester preen wax was secreted almost exclusively by the incubating sex in species with uniparental incubation, and by both sexes in species with biparental incubation. These findings suggest that diester preen waxes have a function that is directly related to incubation. Unexpectedly, in female-incubating Curlew Sandpiper Calidris ferruginea and Buff-breasted Sandpiper Tryngites subruficollis , some males also secreted diester preen waxes during the breeding period. This suggests that some males may in fact incubate, that these waxes may be a remnant from their evolutionary past when both sexes incubated, or that males need to be olfactorally cryptic because they are involved in the making of nest scrapes. The seasonal pattern of preen wax composition was also studied in captive male, female and female-mimicking male ('faeder') Ruff Philomachus pugnax . Captive female Ruff changed preen wax composition from monoesters to diesters in the spring despite the fact that no incubation took place. This suggests that circannual rhythms rather than actual incubation behaviour may trigger the shift to diester waxes. All captive male Ruff, including the faeders, continued to secrete monoesters, supporting the hypothesis that only the incubating sex secretes diesters.     

Epicuticular waxes and flavonol aglycones of the European mistletoe, Viscum album L

Cuticular waxes of Viscum album ssp. album contain oleanolic acid as main constituent, accompanied by aliphatic compounds like alkanes, esters and primary alcohols. A number of flavonol aglycones (methyl ethers of quercetin and kaempferol) have also been identified. Seasonal changes in amount and composition of cuticular waxes and the presence of flavonol aglycones are described and the ecophysiological significance of flavonoids on the surface of the mistletoe is briefly discussed.     

Sex differences in the chemical composition of uropygial gland waxes in domestic ducks

Sexual differences in the chemical composition of the uropygial gland waxes in domestic ducks have been detected before the nesting period. 3-Hydroxy fatty acids containing diester waxes and significant differences in the composition of the fatty acid and alcohol moieties of the monoester waxes occur during February–June only in the female preen wax. Males as well as ducklings, however, show constant wax patterns. Moreover, no significant influence on wax composition of testosterone or estradiol, respectively in male or female ducklings could be verified.     

Monoacylglycerols are components of root waxes and can be produced in the aerial cuticle by ectopic expression of a suberin-associated acyltransferase

The interface between plants and the environment is provided for aerial organs by epicuticular waxes that have been extensively studied. By contrast, little is known about the nature, biosynthesis, and role of waxes at the root-rhizosphere interface. Waxes isolated by rapid immersion of Arabidopsis (Arabidopsis thaliana) roots in organic solvents were rich in saturated C18-C22 alkyl esters of p-hydroxycinnamic acids, but also contained significant amounts of both alpha- and beta-isomers of monoacylglycerols with C22 and C24 saturated acyl groups and the corresponding free fatty acids. Production of these compounds in root waxes was positively correlated to the expression of sn-glycerol-3-P acyltransferase5 (GPAT5), a gene encoding an acyltransferase previously shown to be involved in aliphatic suberin synthesis. This suggests a direct metabolic relationship between suberin and some root waxes. Furthermore, when ectopically expressed in Arabidopsis, GPAT5 produced very-long-chain saturated monoacylglycerols and free fatty acids as novel components of cuticular waxes. The crystal morphology of stem waxes was altered and the load of total stem wax compounds was doubled, although the major components typical of the waxes found on wild-type plants decreased. These results strongly suggest that GPAT5 functions in vivo as an acyltransferase to a glycerol-containing acceptor and has access to the same pool of acyl intermediates and/or may be targeted to the same membrane domain as that of wax synthesis in aerial organs.     

植物角质层蜡质的化学组成研究综述

角质层是植物与外界的第一接触面,而角质层蜡质则是由位于角质层外的外层蜡质和深嵌在角质层中的内层蜡质两部分构成。植物角质层蜡质成分极其复杂,具有重要的生理功能。综述了有关植物角质层蜡质的化学组成信息,探讨了目前植物角质层蜡质化学成分研究中存在的一些问题,展望了角质层蜡质成分的研究前景。     

Xylanase treatment of plant cells induces glycosylation and fatty acylation of phytosterols

Treatment of tobacco suspension cells ( Nicotiana tabacum cv. KY 14) with a purified β -1,4-endoxylanase from Trichoderma viride [1 μg enzyme (ml cells)⁻¹] caused a 13-fold increase in the levels of acylated sterol glycosides and elicited the synthesis of phytoalexins. A commercial preparation of xylanase from Trichoderma viride caused an identical shift in sterols. In contrast, a commerical xylanase from Aureobasidium pullaulans had no effect on the levels of acylated sterol glycosides, but did elevate the levels of sterol esters. Treatment of the cells with Cu²⁺ or Ag⁺ also evoked a severalfold increase in the levels of acylated sterol glycosides. Analysis of the various sterol lipid classes revealed that the large xylanase-induced increase in acylated sterol glycosides occurred at the expense of sterol esters, free sterols and sterol glycosides. Further analyses revealed that the most abundant phytosterol in each of the four classes of sterol lipids was β -sitosterol. Linoleic acid was the most abundant fatty acid in the sterol esters, and palmitic and linoleic acids were the most abundant fatty acids in the acylated sterol glycosides. Glucose was the only sugar moiety in the sterol glycoside and acvlated sterol glycosides. Glucose was the only sugar moiety in the sterol glycoside and acylated sterol glycoside fractions. The results of the present study demonstrate that xylanase from Trichoderma viride induces a dramatic shift in the level of acylated sterol glycosides, indicating that endoxylanase was probably the active component in the cellulase enzyme preparations used in our previous study.     

A comparison of the composition of epicuticular wax from red raspberry (Rubus idaeus L.) and hawthorn (Crataegus monogyna Jacq.) flowers

Epicuticular waxes have been characterised from the flowers of raspberry and hawthorn, on both of which adult raspberry beetles (Byturus tomentosus) can feed. The flower wax from both species had similar alkane profiles and also contained long-chain alcohols, aldehydes and fatty acids. The range of the carbon numbers detected for these classes of compounds was broadly similar in both but the relative amounts of each differed between species. Raspberry flower wax also contained fatty acid methyl esters, a group of compounds that has rarely been detected in plant epicuticular waxes, however, these were not observed in hawthorn flower wax. Long-chain alcohol-fatty acid esters with carbon numbers ranging from C36 to C48 were also detected in both plant species. However, an examination of their constituent acids indicated that in hawthorn the esters based on the C16 fatty acid predominated, whilst in raspberry flower wax, esters based on the C20 fatty acid were most abundant. Both species also contained pentacyclic triterpenoids, which accounted for, on average, over 16 and 48% of the total wax extracted from raspberry and hawthorn flowers respectively. In the former, ursolic and oleanolic acids accounted for over 90% of the pentacyclic triterpenes, whilst hawthorn flower wax, in addition to containing these acids, also contained high relative concentrations of both free and esterified alpha- and beta-amyrins.     

The effects of stress on plant cuticular waxes

Plants are subject to a wide range of abiotic stresses, and their cuticular wax layer provides a protective barrier, which consists predominantly of long-chain hydrocarbon compounds, including alkanes, primary alcohols, aldehydes, secondary alcohols, ketones, esters and other derived compounds. This article discusses current knowledge relating to the effects of stress on cuticular waxes and the ways in which the wax provides protection against the deleterious effects of light, temperature, osmotic stress, physical damage, altitude and pollution. Topics covered here include biosynthesis, morphology, composition and function of cuticular waxes in relation to the effects of stress, and some recent findings concerning the effects of stress on regulation of wax biosynthesis are described.     

Oxidative degradation of model lipids representative for main paper pulp lipophilic extractives by the laccase–mediator system

Different model lipids-alkanes, fatty alcohols, fatty acids, resin acids, free sterols, sterol esters, and triglycerides-were treated with Pycnoporus cinnabarinus laccase in the presence of 1-hydroxybenzotriazole as mediator, and the products were analyzed by gas chromatography. The laccase alone decreased the concentration of some unsaturated lipids. However, the most extensive lipid modification was obtained with the laccase-mediator system. Unsaturated lipids were largely oxidized and the dominant products detected were epoxy and hydroxy fatty acids from fatty acids and free and esterified 7-ketosterols and steroid ketones from sterols and sterol esters. The former compounds suggested unsaturated lipid attack via the corresponding hydroperoxides. The enzymatic reaction on sterol esters largely depended on the nature of the fatty acyl moiety, i.e., oxidation of saturated fatty acid esters started at the sterol moiety, whereas the initial attack of unsaturated fatty acid esters was produced on the fatty acid double bonds. In contrast, saturated lipids were not modified, although some of them decreased when the laccase-mediator reactions were carried out in the presence of unsaturated lipids suggesting participation of lipid peroxidation radicals. These results are discussed in the context of enzymatic control of pitch to explain the removal of lipid mixtures during laccase-mediator treatment of different pulp types.     

Cuticular waxes from potato (Solanum tuberosum) leaves

The qualitative and quantitative compositions of leaf cuticular waxes from potato (Solanum tuberosum) varieties were studied. The principal components of the waxes were very long chain n-alkanes, 2-methylalkanes and 3-methylalkanes (3.1-4.6 microg cm(-2)), primary alcohols (0.3-0.7 microg cm(-2)), fatty acids (0.3-0.6 microg cm(-2)), and wax esters (0.1-0.4 microg cm(-2)). Methyl ketones, sterols, beta-amyrin, benzoic acid esters and fatty acid methyl, ethyl, isopropyl and phenylethyl esters were found for the first time in potato waxes. The qualitative composition of the waxes was quite similar but there were quantitative differences between the varieties studied. A new group of cuticular wax constituents consisting of free 2-alkanols with odd and even numbers of carbon atoms ranging from C25 to C30 was identified.     

Hydrocarbon and multibranched ester waxes from the uropygial gland secretion of grebes (Podicipediformes).

The uropygial gland secretion of some grebes (Podicipediformes) had been shown to contain saturated and unsaturated aliphatic hydrocarbons and monoester waxes. While ester waxes are common constituents of preen gland secretions, nonisoprenoid hydrocarbons have not been detected hitherto. The wax constituents are very complex, belonging to several multibranched homologous series, including unusual acids with ethyl branches. The waxes were identified by gas-liquid chromatography-mass spectrometry and equivalent chain length comparisons. A method for the prediction of equivalent chain length values of unknown methyl esters is offered. The results are discussed from a chemotaxonomic viewpoint.     

Identification of In-Chain-Functionalized Compounds and Methyl-Branched Alkanes in Cuticular Waxes of Triticum aestivum cv. Bethlehem

In this work, cuticular waxes from flag leaf blades and peduncles of Triticum aestivum cv. Bethlehem were investigated in search for novel wax compounds. Seven wax compound classes were detected that had previously not been reported, and their structures were elucidated using gas chromatography-mass spectrometry of various derivatives. Six of the classes were identified as series of homologs differing by two methylene units, while the seventh was a homologous series with homologs with single methylene unit differences. In the waxes of flag leaf blades, secondary alcohols (predominantly C₂₇ and C₃₃), primary/secondary diols (predominantly C₂₈) and esters of primary/secondary diols (predominantly C₅₀, combining C₂₈ diol with C₂₂ acid) were found, all sharing similar secondary hydroxyl group positions at and around C-12 or ω-12. 7- and 8-hydroxy-2-alkanol esters (predominantly C₃₅), 7- and 8-oxo-2-alkanol esters (predominantly C₃₅), and 4-alkylbutan-4-olides (predominantly C₂₈) were found both in flag leaf and peduncle wax mixtures. Finally, a series of even- and odd-numbered alkane homologs was identified in both leaf and peduncle waxes, with an internal methyl branch preferentially on C-11 and C-13 of homologs with even total carbon number and on C-12 of odd-numbered homologs. Biosynthetic pathways are suggested for all compounds, based on common structural features and matching chain length profiles with other wheat wax compound classes.